Alkali Metal Carboxylate as an Efficient and Simple Catalyst for Ring-Opening Polymerization of Cyclic Esters

Alkali metal carboxylates were discovered as efficient and simple catalysts for the ring-opening polymerization of cyclic esters that are alternatives to conventional metal-based catalysts and organocatalysts. In our system using an alcohol initiator and this simple catalyst, biodegradable and biocompatible aliphatic polyesters, such as poly­(lactide), poly­(ε-caprolactone), poly­(δ-valerolactone), and poly­(trimethylene carbonate), were obtained with predictive molecular weights ranging from 3500 to 22 600 and narrow dispersities. A kinetic experiment for the ROP of l-lactide confirmed the controlled/living nature of the present ROP system, which allowed the precise synthesis of end-functionalized polyesters as well as multihydroxyl-containing polyesters, including α,ω-hydroxy telechelic and star-shaped polyesters. Furthermore, a block copolymer containing the poly­(l-lactide) segment was successfully synthesized using a macroinitiator possessing a hydroxyl group at the chain end. The tunability of the alkali metal carboxylates by the appropriate choice of the alkyl moiety and countercation enables not only control of the polymerization behavior but also expansion of the scope of the applicable monomers. Given the low cost, easy handling, and low toxicity of the alkali metal carboxylates, the present ROP system can be highly promising for both laboratory- and industrial-scale polyester productions

Synthesis of Well-Defined Three- and Four-Armed Cage-Shaped Polymers via “Topological Conversion” from Trefoil- and Quatrefoil-Shaped Polymers

This paper describes a novel synthetic approach for three- and four-armed cage-shaped polymers based on the topological conversion of the corresponding trefoil- and quatrefoil-shaped precursors. The trefoil- and quatrefoil-shaped polymers were synthesized by the following three reaction steps: (1) the <i>t</i>-Bu-P₄-catalyzed ring-opening polymerization of butylene oxide using multiple hydroxy- and azido-functionalized initiators to produce the three- or four-armed star-shaped polymers possessing three or four azido groups at the focal point, respectively, (2) the ω-end modification to install a propargyl group at each chain end, and (3) the intramolecular multiple click cyclization of the clickable star-shaped precursors. The topological conversion from the trefoil- and quatrefoil-shaped polymers to the cage-shaped polymers was achieved by the catalytic hydrogenolysis of the benzyl ether linkages that had been installed at the focal point. The amphiphilic cage-shaped block copolymers together with the corresponding trefoil- and quatrefoil-shaped counterparts were synthesized in a similar way using 2-(2-(2-methoxyethoxy)­ethoxy)­ethyl glycidyl ether as a hydrophilic monomer and decyl glycidyl ether as a hydrophobic monomer. Interestingly, significant changes in the critical micelle concentration and micellar morphology were observed for the amphiphilic block copolymers upon the topological conversion from the trefoil- and quatrefoil-shaped to cage-shaped architectures

Chemically Recyclable Unnatural (1→6)-Polysaccharides from Cellulose-Derived Levoglucosenone and Dihydrolevoglucosenone

Unnatural polysaccharide analogs and their biological activities and material properties have attracted considerable research interest. However, these efforts often encounter challenges, especially those related to synthetic complexity and scalability. Here, we report the chemical synthesis of unnatural (1→6)-polysaccharides using levoglucosenone (LGO) and dihydrolevoglucosenone (Cyrene), which are derived from cellulose. Using a versatile monomer synthesis from LGO and Cyrene and cationic ring-opening polymerization, (1→6)-polysaccharides with various tailored substituent patterns are obtained. Additionally, environmentally benign and easy-to-handle organic Brønsted acid catalysts are investigated. This study demonstrates well-controlled first-order polymerization kinetics for the reactive (1S,5R)-6,8-dioxabicyclo[3,2,1]octane (DBO) monomer. The synthesized (1→6)-polysaccharides exhibit high thermal stability and form amorphous solids under ambient conditions, which could be processed into highly transparent self-standing films. Additionally, these polymers exhibit excellent closed-loop chemical recyclability. This study provides an important approach to explore the chemical spaces of unnatural polysaccharides and contributes to the development of sustainable polymer materials from abundant biomass resources

Highly Ordered Cylinder Morphologies with 10 nm Scale Periodicity in Biomass-Based Block Copolymers

Microphase-separated structures of block copolymers (BCPs) have attracted considerable attention for their potential application in the bottom-up fabrication of 10 nm scale nanostructured materials. To realize sustainable development within this field, the creation of novel BCP materials from renewable biomass resources is of fundamental interest. Thus, we herein focused on maltoheptaose-<i>b</i>-poly­(δ-decanolactone)-<i>b</i>-maltoheptaose (MH-<i>b</i>-PDL-<i>b</i>-MH) as a sustainable alternative for nanostructure-forming BCPs, in which both constitutional blocks can be derived from renewable biomass resources, in the case, δ-decanolactone and amylose. Well-defined MH-<i>b</i>-PDL-<i>b</i>-MHs with varying PDL lengths were synthesized through a combination of controlled/living ring-opening polymerization and the click reaction. The prepared MH-<i>b</i>-PDL-<i>b</i>-MHs successfully self-assembled into highly ordered hexagonal cylindrical structures with a domain-spacing of ∼12–14 nm in both the bulk and thin film states. Interestingly, the as-cast thin films of MH-<i>b</i>-PDL-<i>b</i>-MHs (with PDL lengths of 9K and 13K) form horizontal cylinders, with thermal annealing (180 °C, 30 min) resulting in a drastic change in the domain orientation from horizontal to vertical. Thus, the results presented herein demonstrated that the combination of oligosaccharides and biomass-derived hydrophobic polymers appears promising for the sustainable development of nanotechnology and related fields

Multicyclic Polymer Synthesis through Controlled/Living Cyclopolymerization of α,ω-Dinorbornenyl-Functionalized Macromonomers

A novel synthesis of multicyclic polymers that feature ultradense arrays of cyclic polymer units has been developed by exploiting the cyclopolymerization of α,ω-norbornenyl end-functionalized macromonomers mediated by the Grubbs third-generation catalyst (G3). Owing to the living polymerization nature, the number of cyclic repeating units in these multicyclic polymers was controlled to be between 1 and approximately 70 by varying the initial macromonomer-to-G3 ratio. The ring size was also tuned by choosing the molecular weight of the macromonomer; in this way we successfully prepared multicyclic polymers that possess cyclic repeating units composed of up to about 500 atoms, which by far exceeds those prepared to date by cyclopolymerization. Specifically, cyclopolymerizations of α,ω-norbornenyl end-functionalized poly­(l-lactide)­s (PLLAs) proceeded homogeneously under highly dilute conditions (∼0.1 mM in CH₂Cl₂) to give multicyclic polymers that feature cyclic PLLA repeating units on the polynorbornene backbone. The cyclic product architectures were confirmed not only by structural characterization based on NMR, MALDI-TOF MS, and SEC analyses but also by comparing their glass transition temperatures, viscosities, and hydrodynamic radii with their acyclic counterparts. The cyclopolymerization strategy was applicable to a variety of α,ω-norbornenyl end-functionalized macromonomers, such as poly­(ε-caprolactone), poly­(ethylene glycol) (PEG), poly­(tetrahydrofuran), and PLLA-<i>b</i>-PEG-<i>b</i>-PLLA. The successful statistical and block cyclocopolymerizations of the PLLA and PEG macromonomers gave amphiphilic multicyclic copolymers

One-Step Production of Amphiphilic Nanofibrillated Cellulose Using a Cellulose-Producing Bacterium

Nanofibrillated bacterial cellulose (NFBC) is produced by culturing a cellulose-producing bacterium (Gluconacetobacter intermedius NEDO-01) with rotation or agitation in medium supplemented with carboxymethylcellulose (CMC). Despite a high yield and dispersibility in water, the product immediately aggregates in organic solvents. To broaden its applicability, we prepared amphiphilic NFBC by culturing strain NEDO-01 in medium supplemented with hydroxyethylcellulose or hydroxypropylcellulose instead of CMC. Transmission electron microscopy analysis revealed that the resultant materials (HE-NFBC and HP-NFBC, respectively) comprised relatively uniform fibers with diameters of 33 ± 7 and 42 ± 8 nm, respectively. HP-NFBC was dispersible in polar organic solvents such as methanol, acetone, isopropyl alcohol, acetonitrile, tetrahydrofuran (THF), and dimethylformamide, and was also dispersible in poly­(methyl methacrylate) (PMMA) by solvent mixing using THF. HP-NFBC/PMMA composite films were highly transparent and had a higher tensile strength than neat PMMA film. Thus, HP-NFBC has a broad range of applications, including as a filler material

One-Step Synthesis of Poly(amide ester)-Based Block Copolymers with Defined Phase Separation Behavior

We developed a self-switchable, one-step polymerization system based on N-tosylaziridine (TAz)/cyclic anhydride ring-opening copolymerization (ROCOP), cyclic carbonate ring-opening polymerization (ROP), and epoxide/anhydride ROCOP. This system uses a phosphazene-based catalyst for the synthesis of chemical structurally diverse block copolymers. “Block-like” poly(amide ester)s were synthesized by combining two catalytic cycles of TAz/anhydride ROCOP. “Real” block poly(amide ester)-b-polycarbonate and poly(amide ester)-b-polyester were then synthesized by combining TAz/anhydride ROCOP with cyclic carbonate ROP and epoxide/anhydride ROCOP, respectively. Differential scanning calorimetry revealed two glass transition temperatures for the “real” block copolymers, and small-angle X-ray scattering measurements confirmed microphase separation, illustrating a significant difference in polarity between the two blocks of copolymers. These results confirm the precise control of the chemical structure and properties of each block on the synthesized copolymers. This method also enables the comprehensive and synchronous adjustment of the chemical structures of copolymer blocks, a challenge that has received much attention in the field of copolymer synthesis

Sub-10 nm Scale Nanostructures in Self-Organized Linear Di- and Triblock Copolymers and Miktoarm Star Copolymers Consisting of Maltoheptaose and Polystyrene

The present paper describes the sub-10 nm scale self-assembly of AB-type diblock, ABA-type triblock, and A₂B-type miktoarm star copolymers consisting of maltoheptaose (MH: A block) and polystyrene (PS: B block). These block copolymers (BCPs) were synthesized through coupling of end-functionalized MH and PS moieties. Small-angle X-ray scattering and atomic force microscope investigations indicated self-organized cylindrical and lamellar structures in the BCP bulks and thin films with domain spacing (<i>d</i>) ranging from 7.65 to 10.6 nm depending on the volume fraction of MH block (ϕ_MH), Flory–Huggins interaction parameter (χ), and degree of polymerization (<i>N</i>). The BCP architecture also governed the morphology of the BCPs, e.g. the AB-type diblock copolymer (ϕ_MH = 0.42), the ABA-type triblock copolymer (ϕ_MH = 0.40), and the A₂B-type miktoarm star copolymer (ϕ_MH = 0.45) self-organized into cylinder (<i>d</i> = 7.65 nm), lamellar (<i>d</i> = 8.41 nm), and lamellar (<i>d</i> = 9.21 nm) structures, respectively

Biosynthesis of High-Molecular-Weight Poly(d‑lactate)-Containing Block Copolyesters Using Evolved Sequence-Regulating Polyhydroxyalkanoate Synthase PhaC_AR

Bacterial polyhydroxyalkanoate (PHA) synthase PhaCAR is a unique enzyme that can synthesize block copolymers. In this study, poly(d-lactate) (PDLA)-containing block copolymers were synthesized using PhaCAR and its mutated variants. Recombinant Escherichia coli harboring phaCAR and relevant genes were cultivated with supplementation of the corresponding monomer precursors. Consequently, PhaCAR synthesized poly(3-hydroxybutyrate)-b-2 mol % PDLA [P(3HB)-b-PDLA]. The incorporation of the d-lactate (LA) enantiomer was confirmed by chiral gas chromatography. Previously identified beneficial mutations in PhaCAR, N149D (ND), and F314H (FH), which increased activity toward a medium-chain-length substrate 3-hydroxyhexanoyl (3HHx)-CoA, improved the incorporation of LA units. The combined pairwise mutation NDFH synergistically increased the LA fraction to 21 mol % in P(3HB)-b-PDLA. Interestingly, a large amount of LA units (51 mol %) was incorporated by copolymerization with 3HHx units, which yielded P(3HHx)-b-PDLA. The block copolymerization of 3HHx and D-LA units was confirmed by NMR analyses and solvent fractionation of polymers. The PDLA crystal in P(3HHx)-b-PDLA was detected using differential scanning calorimetry and wide-angle X-ray diffraction. Its mass-average molecular weight was 8.6 × 105. Thus, block copolymerization utilized high-molecular-weight PDLA as a component of PHAs

Controlled/Living Ring-Opening Polymerization of Glycidylamine Derivatives Using <i>t</i>‑Bu‑P₄/Alcohol Initiating System Leading to Polyethers with Pendant Primary, Secondary, and Tertiary Amino Groups

The combination of <i>t</i>-Bu-P₄ and alcohol was found to be an excellent catalytic system for the controlled/living ring-opening polymerization (ROP) of <i>N</i>,<i>N</i>-disubstituted glycidylamine derivatives, such as <i>N</i>,<i>N</i>-dibenzylglycidylamine (DBGA), <i>N</i>-benzyl-<i>N</i>-methylglycidylamine, <i>N</i>-glycidylmorpholine, and <i>N</i>,<i>N</i>-bis­(2-methoxyethyl)­glycidylamine, to give well-defined polyethers having various pendant tertiary amino groups with predictable molecular weights and narrow molecular weight distributions (typically <i>M</i>_w/<i>M</i>_n < 1.2). The <i>t</i>-Bu-P₄-catalyzed ROP of these monomers in toluene at room temperature proceeded in a living manner, which was confirmed by a MALDI-TOF MS analysis, kinetic measurement, and postpolymerization experiment. The well-controlled nature of the present system enabled the production of the block copolymers composed of the glycidylamine monomers. The polyethers having pendant primary and secondary amino groups, i.e., poly­(glycidylamine) and poly­(glycidylmethylamine), respectively, were readily obtained by the debenzylation of poly­(DBGA) and poly­(BMGA), respectively, through the treatment with Pd/C in THF/MeOH under a hydrogen atmosphere. To the best of our knowledge, this report is the first example of the controlled/living polymerization of glycidylamine derivatives, providing a rapid and comprehensive access to the polyethers having primary, secondary, and tertiary amino groups